Multi-range transmissions comprising a multi-step main transmission, a following range group, and either an upstream or downstream splitter group, have been known for a while and are mainly used in utility vehicles. For instance, with a two-step designed splitter group within the half of a central gear ratio step, between two consecutive gear ratio steps of the main transmission and the respective gear ratio step, the gear ratio steps of the main transmission are cut in half and the amount of the total available gears of the group transmission is doubled. For instance, through a two-step range group, with transmission ratio step approximately centered between two consecutive transmission ratio steps of the main transmission over the total gear ratio steps of the main transmission and its gear ratio step, the spread of the group transmission is nearly double and the amount of the total, available gears is again doubled.
FIG. 1 shows a scheme of a group transmission of the so-called AS-Tronic family, provided by the applicant. The group transmission presented in FIG. 1 comprises a main transmission HG, a front-mounted front group, or splitter group GV, as well asrange group GP positioned downstream from the main transmission HG. The main transmission HG of the group transmission CT in FIG. 1 is a direct gear transmission of a counter shaft transmission design and has a main shaft WH and two counter shafts WVG1 and WVG2, wherein the first counter shaft WVG1 is connectable to a controllable transmission brake Br.
The main transmission HG has a three-step design with three gear ratio steps G1, G2, and G3 for forward drive, and with a gear ratio step R for reverse drive. Idler gears for the gear ratio steps G1, G2, G3, and R are each rotatably positioned on the main shaft WH and can be shifted via assigned claw clutches. The assigned fixed gears are rotationally fixed on the countershafts WVG1 and WVG2.
The highest gear ratio step G3 of the main transmission HG, which is designed as a direct gear, can be shifted via a direct shift clutch. The shift clutches of the gear ratios G3 and G2, as well as the shift clutches of the gear ratios G1 and R are each combined in a common shift packet S1 or S2, respectively. The main transmission HG can be non-synchronized shifted.
The front group, or splitter group GV of the group transmission CT in FIG. 1 is designed with two-steps, and is also constructed in a countershaft design, wherein the two gear ratio steps K1 and K2 of the front group GV represent two shiftable input constants of the main transmission HG. Due to a small gear ratio difference of the two gear ratio steps K1, K2, the front group GV is designed as a splitter group. The idler gear of the first gear step K1 of the transmission is rotatably positioned on the input shaft WGE which is connected, via a controllable separation clutch K, with a drive aggregate, not shown, which is designed as a combustion engine.
The idle gear of the second gear ratio step K2 is rotatably supported on the main shaft WH. The fixed gears of both gear ratio steps K1, K2 of the front group GV are each rotationally fixed on the counter shafts WVG1 and WVG2 on the input side of the main transmission. The synchronous designed shift groups of the front group GV are combined in a common shift package SV.
The range group GP of the group transmission CT in FIG. 1, which is behind the main transmission HG, is also of a two-step design, but is of a planetary construction having a simple planetary gear set. The sun gear PS is rotationally fixed to the main shaft WH at the output side of the main transmission HG. The planetary carrier PT is rotationally fixed to the output shaft WGA of the group transmission CT. The ring gear PH is connected with a shift package SP which has two synchronous shift clutches through which the range group GP can be shifted alternatively, via a connection between the ring gear PH and the housing, into a low speed drive step L and, via a connection between the ring gear PH and the main shaft WH or the sun gear PS, into a high-speed drive step S. The range group GP is synchronously shifted.
Power can be branched off the countershaft WVG2 of the group transmission CT to drive a power take-off PTO. When power is needed from the group transmission CT to drive the power take-off PTO, it happens during the activation or connection of the power take-off PTO in a way that first an idle rotation speed of the drive aggregate is requested through an engine intervention and thereafter, the transmission is shifted to neutral and the separation clutch K is disengaged and thereafter, the separation clutch K is again engaged and then, when the separation clutch K is again completely engaged, the engine intervention is terminated.
The engagement of the separation clutch K happens in the state of the art as shown in FIG. 2, in which the diagram in FIG. 2 shows a clutch position of the separation clutch K in percent over the time t. At the time t1, the separation clutch K starts engaging when the power take-off PTO is being activated or connected whereupon at the time t2 the separation clutch K is again completely engaged.
In accordance with the state of the art, engagement of the separation clutch K takes place between the time t1 and t2, by means of the characteristic which is dependent on the clutch position, thus, the separation clutch K is completely engaged, in the state of the art, between the time t1 and t2, at a position dependent or distance dependent, respectively, clutch speed.
Due to the fact that the load torque to be assumed by the power take-off PTO is not known, the characteristic curve, through which the separation clutch K is to activate or connect, the power take-off PTO depending on the position or distance needs to be dimensioned so as to prevent the drive aggregate from stalling when the separation clutch K is engaged. Therefore, the separation clutch K is slowly engaged, but this is a disadvantage when lower loads are assumed by the power take-off PTO, because the separation clutch K can here actually be engaged faster. This represents a disadvantage.
An analogous problem arises also when load is diverted from other transmission types to drive an auxiliary drive. Although the invention is presented in conjunction with a group transmission, the application of it is not limited to group transmissions, but can also be used with any transmissions where power can be diverted to drive an auxiliary drive.
Known from DE 197 08 929 A1 is a method to operate a transmission which can be used to drive an auxiliary drive via a countershaft of the group transmission, where a separation clutch can first be disengaged and is thereafter again engaged.